Hyponatraemia

Hyponatraemia can be a little tricky. In this podcast we give you a head start by introducing the topic.

 

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Video Duration: 13 minutes

  • Hyponatraemia
    Created by Nitin Lamba
    General
    Epidemiology

    Serum sodium level < 135mmol/L

    Pathology

    Varied pathology depending on fluid volume status and urinary sodium levels (high levels indicate a renal cause of hyponatraemia, whilst a low cause indicates an extra-renal cause)

    Hypervolaemic hyponatraemia is often seen in patients with cardiac failure, liver cirrhosis or nephrotic syndrome, where there is a reduced ability of the kidneys to excrete water, leading to water retention and therefore dilution of serum sodium.


    Top three causes

    Depends on fluid balance/fluid volume as well as urinary sodium level.

    • If hypovolaemia and hypernaturia, causes are RENAL; most commonly due to EXCESS DIURETIC DOSE, OSMOTIC DIURESIS (e.g. DIABETES) and MINERALOCORTICOID DEFICIENCY
    • If hypovolaemia and hyponaturic, causes are EXTRA-RENAL; most commonly due to VOMITING, DIARRHOEA, BURNS
    • If hypervolaemic and hypernaturia, causes are RENAL; most commonly due to ACUTE/CHRONIC RENAL FAILURE (NEPHROTIC SYNDROME)
    • If hypervolaemic and hyponaturic, causes are EXTRA-RENAL; most commonly due to HEPATIC CIRRHOSIS, ASCITES and CONGESTIVE HEART FAILURE
    • If euvolaemic, common causes are GLUCOCORTICOID DEFICIENCY/STRESS, HYPOTHYROIDISM, SIADH
    Clinical Features
    Symptoms

    Depends on serum sodium level (Mild/moderate/severe)

    If serum sodium = 130-135mmol/L --> Asymptomatic

    If serum sodium = 125-130mmol/L --> Nausea, vomiting, mild confusion

    If serum sodium = 115-125mmol/L --> more pronounced confusion (due to cerebral oedema)

    If serum sodium <115mmol/L --> convulsions, coma

    If hypovolaemic --> vomiting, diarrhoea, use of excessive diuretics

    If hypervolaemic --> h/o cardiac/liver/renal failure

    Signs

    If hypovolaemic

    • prolonged capillary refill
    • tachycardia
    • hypotension (especially postural)
    • dry mucosa
    • reduced skin turgor
    • reduced urine output

    If hypervolaemic

    • raised JVP
    • Bibasal crepitations (pulmonary oedema)
    • Ascites
    • Peripheral oedema


    Investigations
    Cultures

    Urine dipstick, for evidence of proteinuria, haematuria, glucosuria

    Urinary sodium level

    Bloods

    U&Es (to assess serum sodium level, renal function), with calculation of plasma osmolality

    Serum glucose

    LFTs, TFTs


    Imaging

    None

    Scopic/Biopsy

    None

    Functional

    Urinary catheterization and record of fluid balance

    Blood pressure measurements (sitting and standing)


    Treatment
    Conservative

    Depends on fluid status.

    Slow correction required to reduce the risk of Central Pontine Myelinolysis

    In mild hyponatraemia

    • hypovolaemia treated with NORMAL SALINE
    • euvolaemia treated with FLUID RESTRICTION (Limit to 1L/day)
    • hypervolaemia treated with FLUID RESTRICTION and DIURETICS
    Medical

    In mild cases of hypervolaemic hyponatraemia, treat with FLUID RESTRICTION and DIURETIC

    In severe cases of hyponatraemia, consider use of DEMICLOCYCLINE if urinary sodium <125mmol/L or 3% SALINE (hypertonic solution); to be used under specialist guidance only!

    Surgical

    None